The molecular basis for development of highly neutralizing antibodies against HIV is still poorly understood. New approaches are needed to define the molecular and genetic basis for development of B cells specific for HIV, and the antibodies they secrete. We have assembled a strong consortium to attack this research problem. We have developed novel viral and immunologic tools for exploration of the HIV-specific B cell repertoire. The Pi's laboratory has developed efficient techniques for the physical isolation of single virus-specific B cells, and the cloning and expression of antibody genes from these single cells, resulting in panels of human monoclonal antibodies. The Spearman laboratory at Emory has developed production systems for HIV pseudovirion particles that contain fluorescent proteins, allowing presentation of Env sequences of interest in a multivalent display that is conformationally correct and labeled. Dr. Kalams at Vanderbilt has assembled a strong clinical cohort of HIV infected controllers and access to rapid progressors, from whom we will obtain blood specimens for comparative purposes. We will test the hypothesis that HIV controllers exhibit a B cell repertoire characterized by broader use of VH segments than the oligoclonal repertoire of rapid progressors, and more importantly, a greater degree of somatic hypermutation that results in higher affinity antibodies with more neutralizing potency. We will determine the molecular genetics of the antibody genes from HIV-specific cells from these two subject classes, and determine the repertoire changes over time. We will determine the effect of the genetic changes observed on the neutralizing function of the monoclonal antibodies that we isolate. A major collateral benefit of these basic science studies aimed at understanding repertoire development is that the work also will result in production of large panels of human monoclonal antibodies that could be of therapeutic or prophylactic benefit. The most potent antibodies also will be used to define epitopes of interest, guiding vaccine design efforts. Public health: These studies will define how effective antibodies to HIV are generated in humans. The studies will help us to understand if it is feasible to find antibodies in infected humans that kill virus.